One-time programmable cells, so-called “OTPs”, are used multifariously in semiconductor technology. They are used to allow the user to put a semiconductor chip into a state, which he desires and which is then intended to be no longer capable of being changed. To this end, one or an arbitrary number of one-time programmable cells may be arranged on one chip. Said cells may in this case be connected in order, for example, to be able to program a number (which results from the number of cells) in accordance with the bits available. Prescribed characteristics which are intended to be no longer capable of being changed may likewise be subsequently programmed using particular cells. This is effected to such an extent that, in the case of so-called DRAM modules having redundant memory cells, for example, one-time programmable memory cells are used to program access possibilities in such a manner that areas having defective memory cells are blocked, with the result that the latter are no longer accessed.
In the case of one-time programmable cells, a distinction is usually made between so-called “fuses” and so-called “anti-fuses”. The so-called “fuse” corresponds to a line interruption, while the so-called “anti-fuse” corresponds to the production of a line connection. The programmed state of the “fuse” or “anti-fuse” is ascertained, for example, by ascertaining a voltage drop across said cell or the current flow through said cell. In the case of a so-called “fuse”, a current flow may be detected in the unprogrammed state when the voltage drop is minimal, these electrical characteristic quantities being reversed in the programmed state, with the result that, in the programmed state, a high voltage drop then appears when the current flow is minimal. In the case of the so-called “anti-fuse”, the electrical characteristic quantities are exactly the inverse of those of the so-called “fuse” in the unprogrammed and programmed states. One-time programmable cells of this type and circuits for programming them are described, for example, in US2002/0190348A1, EP1233453A2 and DE 100 26 251 A1. These one-time programmable cells are usually programmed using an increased voltage or an increased current, so that a previously existing state is irreversibly destroyed.
However, depending on the type of programmable cell, it also happens often enough that the transition from conductive to non-conductive or vice versa is not permanently 100% achieved. This means that, for example when there is not 100% destruction, the cell changes its state toward the unprogrammed state during operation as a result of migration.
This problem has hitherto been circumvented by designing the “fuses” and “anti-fuses” to be so sensitive that programming is carried out using a very high safety/security margin since reprogramming was impossible. This is particularly disadvantageous when, in the case of a component having a long lifetime, the programming is changed in the course of operation, for example as a result of electromigration, as previously indicated. In many applications, this means a reduction in the operational reliability of the component.